1. Field of the Invention
This invention relates to conversion of plutonium nitrate into plutonium dioxide and more particularly refers to a new and improved method and apparatus for producing a purer plutonium dioxide by discontinuous precipitation of plutonium oxalate from plutonium nitrate containing americium as an impurity.
2. Background of the Invention
Discontinuous precipitation of plutonium oxalate from plutonium nitrate-nitric acid solution within a reaction vessel, by means of solid oxalic acid or solid ammonium oxalate, with subsequent separation of the plutonium oxalate from the residual liquid and calcination of the precipitate is known. The end product is PuO.sub.2. Such a process is also called conversion of plutonium nitrate into plutonium dioxide. The plutonium nitrate is produced in the processing of burned-up fuel assemblies and is the starting product for the fabrication of plutonium-containing nuclear reactor fuel rods. Such a conversion plant is described in the journal "Kerntechnik". vol. 15, 1973, pages 257 to 263.
The method in the literature reference, however, was not found entirely satisfactory. In addition to desired improvements in the process cycle it was found that the plutonium nitrate feed contained americium as a contaminant which passed into the precipitate of plutonium oxalate resulting in an impure plutonium product. The decontaminant is the decay product of plutonium-241, namely, americium-241, which is a gamma radiator, which generally varies in amount from a fraction of a percent to several percent.